The isolation and identification of a tryptophan photo-oxidation product which is mutagenic and cell-lethal for recombinationless bacterial mutants is being carried out. This involves utilization of chromatographic techniques, such as gel permeation and high pressure liquid chromatography, to obtain homogeneous samples of the active material. Identification of the pure substances(s) will rest on spectral and chromatographic techniques, with chemical confirmation by synthesis or by transformation to a known compound. Finally, after positive identification has been made, effective means of producing the active material will be developed to supply quantities required for experiments concerning the interaction with biomolecules which gives rise to the observed biological activity.